Recent research on bacterial gene acquisition by the P1 chromosome has yielded the following results: hybridizations of P1 and bacterial genes do occur in recipients for generalized transduction; a transient induction of lytic functions of a recipient's P1 plasmid is essential for or markedly facilitates the acquisition process; the formation of the hybrid prophage can be detected in recipients with single site defects (as opposed to extensive deletions); the acquisition can render the hybrid prophage too large to be wholly encapsidated in a single bacteriophage P1 capsid; some hybrid prophage have a cis dominant P1 genetic defect, which is tentatively identified as a deletion for a site governing rolling circle replication and resultant concatemer formation. A working hypothesis accommodating these observations has been developed. DNA ends are susceptible to genetically aberrant fusion processes. In a transiently induced lysogen a P1 concatemer is generated. If a transduced chromosome fragment is present in the cell, a genetically hybrid chromosome is sometimes defined through two successive fusions of fragment and P1 concatemer ends. The proposed research program is comprised of the following constituents: tests to determine if bacterial genes from any host chromosomal region can become constituents of specialized transducing P1 derivatives; examination of the role of host DNA recombination systems in acquisition processes; the isolation of P1 mutants with acquisition (acq) defects; genetic and biophysical characterization of acq mutants; exploratory programs for the biophysical isolation and characterization of intermediates in acquisition.